The Categories section is found in the left side panel together with the other main sections in the software.
In the Categories section, click on + New Category to create a new category.
Then you can name your category and choose the color of its button in the Button Color dropdown menu.
The name of the category and its button color that you can set here also sets the category button's appearance on the directories. You can see the button's preview at the end of the button color field.
Once you have created your category, you can then assign your offers to it by editing your offers.
Once you've assigned your offers to the category, the category button will now show up on the Directory campaign that the offers are part of. When you click on the category button, it will filter the directory offers and show the offers that are assigned to that category.